I've been thinking about ways to buy less grow bed material
and keep the media simpler and/or lighter. Do people do layered
designs? That is, how about placing a screen X inches above the
bottom, then a layer of mat/foam media, then topped with a light
material like hydroton or expanded shale?

This way, there would be very high biological surface area in the
mat/foam, and there wouldn't be so much aggregate media to
buy, maintain, etc. The roots could just hang in water-filled space
below the foam.

And, what of irrigation. I'd like to water them under pressure. Is it
reasonable to water a media bed using runners off a poly pipe
like some people do with foam filled towers? It seems I'd just need
enough little feeder lines to achieve the desired GPH.

As for the siphon drain system, I was thinking of having the siphon
or flout in a small separate box connected low in the bed with a
removable grate and/or filter so I just have to clean that periodically
instead of having to remove the siphon/flout.

What do you think? Bad ideas? Are there highly preferred alternatives?